Thiolcarbamate derivatives are widely used in agricultural practice as active ingredients of effective herbicides. Thiolcarbamates and herbicide compositions containing those are reported e.g. in the U.S. Pat. Nos. 2,913,327 and 3,175,8987. Out of these compounds, S-ethyl N,N-dipropylthiolcarbamate (EPTC), S-propyl N,N-dipropylthiolcarbamate (vernolate) and S-ethyl N,N-diisobutylthiolcarbamate (butylate) are widely used in the agricultural practice.
However, in addition to the outstanding herbicidal effect, the thiolcarbamates may damage the useful cultivated plants. To prevent this effect they are frequently combined with antidotes (protecting agents). Antidotes, useful against the damaging and particularly the maize-damaging effect of herbicide compositions containing thiolcarbamate derivatives, are disclosed e.g. in the Belgian Pat. Nos. 782,120 and 806,038, in the U.S. Pat. Nos. 3,893,838 and 3,931,313 as well as in the Hungarian Pat. Nos. 165,736, 176,784 and 168,977. Out of the antidotes, N,N-diallyldichloroacetamide, reported in the Hungarian Pat. No. 165,736 has most widely been used in the agricultural practice.
By using antidotes, an appropriate selectivity is associated with the excellent herbicidal activity of the compositions containing thiolcarbamate derivatives. Concerning the possibilities for utilizing antidotes, the special literature and particularly the above-cited patent specifications are to be mentioned.
In addition to the advantageous herbicidal activity and appropriate selectivity, also the optimum duration of the activity represents a further important requirement to herbicides.
Herbicide compositions containing thiolcarbamate derivatives are in most cases sprayed on the soil surface before sowing. The concentration of the thiolcarbamate derivatives is high in the upper layer of the soil, thus the herbicidal effect is most intense just after spraying. However, the concentration of the thiolcarbamate derivatives rapidly decreases in the soil because of a number of factors, whereby after a few days they are practically undetectable.
One reason for this concentration decrease is the volatility of the active ingredients. This can be avoided by embedding the herbicide to a depth of 5 cm in the soil after having sprayed them upon the soil surface.
Another reason for the losses is the rapid decomposition of the thiolcarbamate derivatives in the soil caused by microbial and physico-chemical factors. This decomposition appears to be more rapid in fields, where thiolcarbamate-type herbicides have earlier and repeatedly been applied.
The rapid decomposition of thiolcarbamates in the soil can be prolonged by using so-called extenders, whereby the herbicidal activity and duration of the activity of the thiolcarbamates are significantly enhanced. Thus weed control becomes more effective and economical than earlier.
Herbicide compositions containing also extenders are reported in the published Hungarian patent application Nos. 783/82 and 3383/82. According to the former patent application, in addition to the thiolcarbamate active ingredients various substituted 4-phenyl-1,2,3-thiadiazole derivatives are applied on the soil, while according to the latter patent application tertiary amines, e.g. diallylamine are used. The rate of decomposition of the thiolcarbamate derivatives is significantly diminished by the use of the above compounds to result in a prolonged action.
According to the methods known in the art, the extenders are used in an amount of 2 to 4 ppm as calculated for the soil.
It is an important requirement, that the extenders used in the practice should be simply producible and cheap. Further on, these extenders should act in low doses and should effectively promote the action of the thiolcarbamates. However, the extenders known so far do not completely satisfy these practical requirements.